Project Summary/Abstract The disruption of oxygen homeostasis is a crucial feature in the pathophysiology of many common and devastating diseases, including heart disease, chronic lung disease, and cerebrovascular disease. Highland natives of the Tibetan plateau, whose ancestors arrived ~25,000 years ago, are protected from high incidence of disease related to low oxygen availability (hypoxia) in part because they have evolved a reduced responsiveness to its harmful effects. The genetic basis of hypoxia adaptation in Tibetans is related to natural selection at the gene epas1, a master regulator of the hypoxia-inducible factor (HIF) pathway that controls physiological responses to hypoxia. Dissection of the mechanisms by which selection at epas1 results in beneficial responses to hypoxia is hampered by the lack of a tractable model, but will ultimately provide key insights into novel therapies related to the loss of oxygen homeostasis. In this series of studies, I will use the deer mouse (Peromyscus maniculatus) to test the hypothesis that genetic variation at epas1 facilitates adaptive cardiorespiratory responses to hypoxia, and to detail the molecular mechanisms that underlie such adaptations. Deer mice live at both high- and low-altitudes, and like highland Tibetans, natural patterns of allele frequency variation suggest that epas1 has been a target of selection in high-altitude populations. I will link epas1 genetic variation to adaptive cardiorespiratory changes by breeding mice of known epas1 genotype under hypoxia and testing for effects on heart, lung, and blood function and Darwinian fitness (Aim 1). I will then use RNA-seq and protein expression assays to characterize the molecular mechanisms underlying physiological effects of epas1 variation at high-altitude by associating genotypic differences in HIF-cascade regulation with differences in cardiorespiratory function (Aim 2). Finally, I will verify that experimental results are applicable in a natural context by associating genetic variation at epas1 with cardiorespiratory physiology and gene expression in a wild, admixed population of high-altitude mice (Aim 3). This work will advance our understanding of the mechanisms of adaptation to high-altitude, which may in turn provide novel insights into therapeutic strategies for hypoxia-related disease.